Report on Akan (Japan) — 24 September-30 September 2008
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 24 September-30 September 2008
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2008. Report on Akan (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 24 September-30 September 2008. Smithsonian Institution and US Geological Survey.
43.384°N, 144.013°E; summit elev. 1499 m
All times are local (unless otherwise noted)
Seismic tremor from the Akan volcanic complex that lasted for four minutes on 29 September prompted JMA to raise the Alert Level from 1 to 2 (using a 1-5 scale). The number of earthquakes had increased since 26 September. A white plume rose less than 100 m above the Me-Akan volcano group. [Correction: The numbered Alert Level system was not applied to Akan. Instead, a near-crater warning was issued.]
Geological Summary. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.